Warmup22.java

public int mystery(int n)
{
    int a = 0, b = 1;
    while (n > 0)
    {
        n--;
        b = b+a;
        a = b-a;
        
        if ((a + b) % 13 == 0)
        {
            return n;
        }
    }
    
    return -1;
    
}